The present disclosure is directed to gas metering apparatus and more particularly to apparatus which measures gas with a high level of precision. It is particularly intended for use with a small volume, small flow gas source, but by choosing appropriate motor, cylinder size and pressure response the system can be extended to high gas volume and rates. Several examples of such a device in use and operation should be noted. First of all, it is necessary often to measure a small quantity of gas devolved from a chemical process. Assume as an example that a specified quantity of materials are placed in a closed beaker. Assume that they generate a specific gas volume. If the beaker is small and the gas volume is likewise small, precise and accurate measurement is required to obtain an indication of conversion in the process. The present apparatus assists in measuring such a small volume. Another circumstance in which small volumetric gas flows are measured is the situation in which a solid core sample is retrieved from a well. Assume further that gas entrained in the core sample must be measured. The core sample will devolve gas over a period of time. The volume of gas is quite small. It must be accurately measured during the collection of gas for the purpose of properly determining values and significance of the core sample data. The present apparatus is such an accurate measuring system. It is a gas metering collection apparatus for use in conjunction with a low pressure, low flow rate source. This is particularly useful in laboratory test circumstances. The apparatus has a piston and cylinder which draw the sample in. The displacement of the cylinder is precisely measured and the stroke of the piston is also precisely controlled. This defines a fixed or known volume. The apparatus also includes a transducer which measures the pressure in this volume so that it is fixed or set. The cylinder is provided in duplex, and a valving system is connected so that first one cylinder and then the other is charged to assure that the gas flow is continuously received and measured. A summation system is likewise included to represent the output and to convey the measured volume in some suitable calibrated indication. Typically, the volume is set at a specified pressure and is indicated in milliliters. While the foregoing speaks generally of the foregoing apparatus, a more detailed description is set forth below upon reference to the drawings of the apparatus.